Communication control system, communication control method, communication control apparatus and communication control program

ABSTRACT

A communication control system includes a plurality of layer 2 switches (SWs); and a communication control device that controls communication of the SWs. Each SW includes one or more queues that each have a variable queue length for accumulating input frames, and a transmission unit that has a shaping function of transmitting the frames accumulated in the queues to a desired destination at a desired rate. The communication control device includes a correction processing unit that acquires an amount of discarded data generated in each queue of the SW, and multiplies the acquired amount of discarded data by a correction coefficient weighted by the cumulative number of times of discarding occurrences for which the amount of discarded data is not 0 to obtain a corrected amount of discarded data; and an adjustment processing unit that determines adjustment values for the queue length of each queue and shaping rate of the SW based on the corrected amount of discarded data, and notifies each SW of the adjustment values.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 U.S. National Phase of InternationalApplication No. PCT/JP2020/017947 filed on Apr. 27, 2020, which claimspriority to Japanese Application No. 2019-090105 filed on May 10, 2019.The entire disclosures of the above applications are incorporated hereinby reference.

TECHNICAL FIELD

The present invention relates to a communication control system, acommunication control method, a communication control device, and acommunication control program for leveling microbursts generated in alayer 2 network (L2NW) including a layer 2 switch (SW).

BACKGROUND ART

Communication terminals for IoT (Internet of Thing) (hereinafterreferred to as IoT terminals) are arranged in various places dependingon the purpose. These IoT terminals are connected to a server(hereinafter referred to as an IoT server) via a radio base station ordedicated gateway device (hereinafter referred to as an IoT-GW), anddata is transmitted and received in accordance with instructions fromthe IoT server.

FIG. 6 illustrates a configuration example of a conventionalcommunication control system.

In FIG. 6 , each IoT terminal is connected to an IoT-GW by wirelesscommunication or wired communication. Each IoT-GW performs bidirectionalcommunication with an IoT server via a layer 2 network (L2NW) includinglayer 2 switches (SWs).

In the L2NW, a connection path for exclusive communication is formed inadvance among IoT-GW #1, IoT-GW #2, and IoT server #1. In FIG. 6 , theidentifier (flow ID) of the path is set to 100. Data from IoT-GW #1 isassigned at least a flow ID of 100 at SW #0, which is the entrance ofthe L2NW, and is transferred to the next SW to which the date is to betransferred in accordance with a transfer routing table. Here, thetransfer routing table describes a transfer routing path for each flowID.

In this L2NW transfer, a plurality of IoT-GWs may be accommodated in thesame flow ID. Therefore, for example, when pieces of data for connectionrequests from a plurality of IoT terminals to the same IoT server aresimultaneously generated on the same flow ID, the pieces of data aresubjected to time multiplexing on the L2NW, and reaches the IoT serverin the form of a microburst, which is a burst of traffic in a shortperiod of time in milliseconds. As a result, the input traffic to theIoT server momentarily exceeds the processing speed, so that data isdiscarded, and it is necessary to resend the data from the IoT terminal.

In order to prevent this issue, it is necessary to reduce (level) themicroburst to the maximum processing speed or less of the IoT server andinput it to the IoT server (NPL 1). However, since it is difficult toknow in advance which SW the microburst originates from, it is necessaryfor each SW to have a large-capacity buffer for microburst leveling,which increases the construction cost of the L2NW.

Therefore, NPL 2 discloses a method of pooling, as a resource that canbe allocated, a memory for buffer originally mounted on each SW in agroup of SWs on a transfer path, and adjusting the resource allocationamount of the pooled memories according to a generated microburst, sothat it is possible to level the microburst up to a target rate (maximumprocessing rate of the IoT server) without increasing the size of thebuffer memory mounted on each SW.

FIG. 7 illustrates an example of changing the resource allocation amountdisclosed in NPL 2.

In FIG. 7 , each SW in the L2NW includes the same number of queues asthe number of flow IDs, and accumulates transfer frames for each flowID. Each SW also includes a transmission unit having a shaping function(shaper) for leveling the accumulated frames to a designated shapingrate for each flow ID and outputting the resulting frames. In FIG. 7 ,(a) illustrates an example before the resource allocation amount ischanged, and in FIG. 7 , (b) illustrates an example after the resourceallocation amount is changed.

As illustrated in (a) of FIG. 7 , the required value of the input rateto the IoT server is set to 1 Gbps, and the initial value of theleveling rate of each of SW #0, SW #1, and SW #2 for the flow is alsoset to 1 Gbps. Further, the initial value of the queue length of each SWfor the flow is set to 1 Mbit, and the input traffic to SW #0 is amicroburst in which 5 Gbps continues for 1 ms. When the microburstoccurs, the required amount of accumulated data of SW #0 is(Input 5 Gbps−Output 1 Gbps)×Burst Length 1 ms=4 Mbit.

However, since the queue length of SW #0 is 1 Mbit, queue overflowoccurs, so that data of 3 Mbit is discarded. On the other hand, in SW #1and SW #2, since the input/output rate is 1 Gbps, data of 1 Mbit issequentially transferred, so that data is not discarded.

In order to prevent the recurrence of discarding at SW #0, in the methodaccording to NPL 2, the resource allocation amount is adjusted so thatthe discarded data is distributed and buffered in the queues of the SWson the transfer path, as illustrated in (b) of FIG. 7 . Specifically,the queue length of SW #0 is set to 2 Mbit by being increased by 1 Mbitso that the discarded data amount of 3 Mbit is distributed and bufferedin three SWs on the transfer path by 1 Mbit, and the shaping rate of SW#0 is set to 3 Gbps so that queue overflow does not occur. As a result,the amount of accumulated data of SW #0 is(Input 5 Gbps−Output 3 Gbps)×Burst Length 1 ms=2 Mbit.

In SW #1 in the next stage, it already has a queue length of 1 Mbit, thequeue length is not changed, and the shaping rate is set to 2 Gbps toreduce the amount of data to be buffered in the queue to 1 Mbit or less.As a result, the amount of accumulated data of SW #1 is(Input 3 Gbps−Output 2 Gbps)×Burst Length 1 ms=1 Mbit.

In SW #2 in the next stage, since it originally has a queue length of 1Mbit and the amount of data to be buffered in the queue is also 1 Mbit,there is no change. As a result, the amount of accumulated data of SW #2is(Input 2 Gbps−Output 1 Gbps)×Burst Length 1 ms=1 Mbit.

In this way, a buffer memory resource of 4 Mbit which is required forleveling the microburst is secured on the transfer path.

A communication control device (L2NW controller: L2NWC) is arranged onthe L2NW to determine the resource adjustment value. The L2NWCsequentially acquires the amount of discarded data for each flow ID fromeach SW, determines adjustment values for the queue length and shapingrate each time data is discarded, and notifies each SW to change them.

CITATION LIST Non Patent Literature

-   [NPL 1] Anzai et al., “Development of 10 Gbits/s Traffic Shaper”,    Anritsu Technical, No. 88, 2013.3-   [NPL 2] Uzawa et al., “5G/IOT Jidai No Multi-service Shuuyou Raiya 2    (Layer-2 Network Control Techniques for Multi-service Accommodation    toward 5G/IoT era)”, IEICE Technical Report, CS2018-47

SUMMARY OF THE INVENTION Technical Problem

The resource adjustment disclosed in NPL 2 requires that the L2NWCperiodically collects the amounts of discarded data for each flow IDfrom each SW. It is difficult to make this collection cycle less thanthe total value of the round-trip propagation delay between the L2NWCand each SW, the transfer delay between the L2NWC and each SW, theinternal processing delay of each SW, and the internal processing delayof the L2NWC, and the total value may be several tens of milliseconds toa few seconds. Therefore, there is a possibility that a plurality ofmicrobursts may occur in the same flow within one cycle. In that case,the amount of discarded data is the integrated value of the amounts ofdiscarded data generated for the respective microbursts. Therefore, ifthe adjustment values for the queue length and shaping rate of the SWare determined based on the integrated value of the amounts of discardeddata, then the resources may be over allocated.

The present invention is to provide a communication control system, acommunication control method, a communication control device, and acommunication control program which are capable of preventing resourcesfrom being over allocated and efficiently leveling microbursts even in acase where the interval of collecting the amount of discarded data foreach flow ID from each SW is long.

Means for Solving the Problem

According to a first invention, a communication control system includesa plurality of layer 2 switches (SWs); and a communication controldevice that controls communication of the SWs, wherein each SW includesone or more queues that each have a variable queue length foraccumulating input frames; and a transmission unit that has a shapingfunction of transmitting the frames accumulated in the queues to adesired destination at a desired rate, and the communication controldevice includes a correction processing unit that acquires an amount ofdiscarded data generated in each queue of the SW, and multiplies theacquired amount of discarded data by a correction coefficient weightedby the cumulative number of times of discarding occurrences for whichthe amount of discarded data is not 0 to obtain a corrected amount ofdiscarded data; and an adjustment processing unit that determinesadjustment values for the queue length of each queue and shaping rate ofthe SW based on the corrected amount of discarded data, and notifieseach SW of the adjustment values.

In the communication control system according to the first invention,the correction coefficient may be managed for each SW and for eachqueue, and may be a value with an upper limit of 1 that increases by β(β<1) each time the cumulative number of times of discarding occurrencesincreases. Further, the correction coefficient may be α smaller than βwhen the cumulative number of times of discarding occurrences is 1.

In the communication control system according to the first invention,the correction coefficient may be managed for each SW and for eachqueue, and may be a value with an upper limit of 1 that increases by βdaccording to the cumulative number of times of discarding occurrences d,and β1<β2<. . . <β(N−1)<βN or β1>β2>. . . >β(N−1)>βN may be set, where Nis the cumulative number of times of discarding occurrences when thecorrection coefficient reaches 1.

In the communication control system according to the first invention,the correction processing unit may perform processing of stoppingincrementing the cumulative number of times of discarding occurrenceswhen the amount of discarded data becomes 0, and of decrementing thecumulative number of times of discarding occurrences when the cumulativenumber of times of not-discarding occurrences in which the amount ofdiscarded data is 0 exceeds a specified value, after the cumulativenumber of times of discarding occurrences reaches 1 or more.

In the communication control system according to the first invention,the correction processing unit may set as an initial value a correctioncoefficient based on an immediately preceding correction coefficientwhen the amount of discarded data becomes 0, and obtain a correctioncoefficient weighted by the cumulative number of times of discardingoccurrences reset, after the cumulative number of times of discardingoccurrences reaches 1 or more.

According to a second invention, a communication control methodperformed by a communication control system that includes a plurality oflayer 2 switches (SWs), and a communication control device that controlscommunication of the SWs, each SW including one or more queues that eachhave a variable queue length for accumulating input frames, and atransmission unit that has a shaping function of transmitting the framesaccumulated in the queues to a desired destination at a desired rate,the communication control method including: by the communication controldevice, acquiring an amount of discarded data generated in each queue ofthe SW; multiplying the acquired amount of discarded data by acorrection coefficient weighted by the cumulative number of times ofdiscarding occurrences for which the amount of discarded data is not 0to obtain a corrected amount of discarded data; determining adjustmentvalues for the queue length of each queue and shaping rate of the SWbased on the corrected amount of discarded data; and notifying each SWof the adjustment values.

According to a third invention, a communication control device for acommunication control system that includes a plurality of layer 2switches (SWs), and the communication control device that controlscommunication of the SWs, each SW including one or more queues that eachhave a variable queue length for accumulating input frames, and atransmission unit that has a shaping function of transmitting the framesaccumulated in the queues to a desired destination at a desired rate,the communication control device being configured to acquire an amountof discarded data generated in each queue of the SW; multiply theacquired amount of discarded data by a correction coefficient weightedby the cumulative number of times of discarding occurrences for whichthe amount of discarded data is not 0 to obtain a corrected amount ofdiscarded data; determine adjustment values for the queue length of eachqueue and shaping rate of the SW based on the corrected amount ofdiscarded data; and notify each SW of the adjustment values.

A communication control program according to a fourth invention causes acomputer to execute processing performed by the communication controldevice according to the third invention to acquire an amount ofdiscarded data generated in each queue of the SW; multiply the acquiredamount of discarded data by a correction coefficient weighted by thecumulative number of times of discarding occurrences for which theamount of discarded data is not 0 to obtain a corrected amount ofdiscarded data; and determine adjustment values for the queue length ofeach queue and shaping rate of the SW based on the corrected amount ofdiscarded data.

Effects of the Invention

According to the present invention, it is possible to prevent resourcesfor the queue length and shaping rate of the SWs from being overallocated and efficiently level microbursts even in a case where theinterval of collecting the amount of discarded data for each flow IDfrom each SW is long.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a configuration example of acommunication control system according to the present invention.

FIG. 2 is a diagram illustrating an outline of updating a correctioncoefficient C(f, n) in a first embodiment.

FIG. 3 is a diagram illustrating an outline of updating a correctioncoefficient C(f, n) in a second embodiment.

FIG. 4 is a diagram illustrating an outline of updating a correctioncoefficient C(f, n) in a third embodiment.

FIG. 5 is a diagram illustrating an outline of updating a correctioncoefficient C(f, n) in a fifth embodiment.

FIG. 6 is a diagram illustrating a configuration example of aconventional communication control system.

FIG. 7 illustrates an example of changing the resource allocation amountdisclosed in NPL 2.

DESCRIPTION OF EMBODIMENTS

A feature of the present invention is to correct the amount of discardeddata collected for each flow from each SW of an L2NW by a methoddescribed below, and determine adjustment values for the queue lengthand shaping rate of each SW based on the amount of discarded data aftercorrection (corrected amount of discarded data). The present inventionis different from that of NPL 2 in this feature.

FIG. 1 illustrates a configuration example of a communication controlsystem according to the present invention.

In FIG. 1 , an L2NWC is connected to SW #0 to SW #3 which make up anL2NW. Each SW in the L2NW includes the same number of queues as thenumber of flow IDs, and accumulates transfer frames for each flow ID.Each SW also includes a transmission unit having a shaping function forleveling the accumulated frames to a designated shaping rate for eachflow ID and outputting the resulting frames.

The L2NWC includes a correction processing unit 11 that outputs acorrected amount of discarded data obtained by correcting the amount ofdiscarded data collected for each flow ID from each SW, and anadjustment processing unit 12 that determines adjustment values for thequeue length and shaping rate of each SW for each flow ID based on thecorrected amount of discarded data.

The correction processing unit 11 updates a correction coefficient C(f,n) each time an amount of discarded data is collected, where f is a flowID and n is the number of an SW, and then the correction processing unit11 outputs a corrected amount of discarded data obtained by multiplyingthe amount of discarded data collected for each flow ID from each SW bythe updated correction coefficient C(f, n). Note that the correctioncoefficient C(f, n) is a different value for each SW and each flow ID.

The adjustment processing unit 12 treats the corrected amount ofdiscarded data output by the correction processing unit 11 for each SWand each flow ID as the amount of discarded data collected from each SW,determines the adjustment values for the queue length and shaping rateof each SW for each flow ID in the same manner as in NPL 2, and notifieseach SW of the adjustment values.

First Embodiment

FIG. 2 illustrates an outline of updating the correction coefficientC(f, n) in a first embodiment.

In FIG. 2 , the horizontal axis represents the cumulative number oftimes of discarding occurrences d, which is the cumulative number oftimes the amount of discarded data collected for the flow ID: f from SW#n was not 0. The vertical axis is the correction coefficient C(f, n)collected for the flow ID: f from SW #n, where the correctioncoefficient is β for a cumulative number of times of discardingoccurrences d of 1 and increases by 3 each time the cumulative number oftimes of discarding occurrences d increases by 1, and its upper limitis 1. Accordingly, the correction coefficient C(f, n) is given by thefollowing equation.C(f,n)=min(1,d×β)

Here, β is a predetermined value, and for example, in a case where thecumulative number of times of discarding occurrences when the correctioncoefficient C(f, n) reaches the upper limit of 1 is set to N, it isrepresented asβ=1/N.

As illustrated in FIG. 2 , the correction coefficient C(f, n) isweighted according to the cumulative number of times of discardingoccurrences d. In other words, the correction coefficient C(f, n) at theearly stage for the cumulative number of times of discarding occurrencesd is significantly smaller than 1, and the corrected amount of discardeddata obtained by multiplying the amount of collected discarded data bythe correction coefficient C(f, n) is also small. This makes it possibleto avoid over-allocation to respective SWs based on the amount ofdiscarded data before correction. Further, as the cumulative number oftimes of discarding occurrences d increases, the correction coefficientC(f, n) increases, and the corrected amount of discarded data alsoincreases. As a result, the corrected amount of discarded dataapproaches the amount of discarded data before correction, so that theoccurrence of data discarding can be suppressed by appropriatelyadjusting the resources for the SWs. Further, it is possible not only toprevent a situation in which a large number of allocation changes(changes in the queue length and shaping rate) occur in the adjustmentprocessing unit 12 despite traffic conditions similar to those ofmicrobursts that have occurred in the past, but also to prevent asituation in which an excessive allocation change is made to amicroburst under a traffic condition that has never occurred in thepast.

Here, when the correction coefficient C(f, n), which increases accordingto the cumulative number of times of discarding occurrences d, exceeds1, the cumulative number of times of discarding occurrences d is resetto 0. Further, the corrected amount of discarded data obtained bymultiplying the correction coefficient C(f, n) is suppressed to be equalto or less than the maximum amount of discarded data that can occur inone microburst.

Second Embodiment

FIG. 3 illustrates an outline of updating the correction coefficientC(f, n) in a second embodiment.

In FIG. 3 , the horizontal axis represents the cumulative number oftimes of discarding occurrences d. The vertical axis is the correctioncoefficient C(f, n) collected for the flow ID: f from SW #n, and thecorrection coefficient increases by βd according to the cumulativenumber of times of discarding occurrences d. Accordingly, the correctioncoefficient C(f, n) is set asβ1, β2, . . . , β(N−1), βNaccording to the cumulative number of times of discarding occurrences d.Here, N is the cumulative number of times of discarding occurrences whenthe correction coefficient C(f, n) reaches 1, andβ1<β2<. . . <β(N−1)<βNmay be set so that the rate of increase in the correction coefficientC(f, n) increases as the cumulative number of times of discardingoccurrences d increases. Orβ1>β2>. . . >β(N−1)>βNmay be set so that the rate of increase in the correction coefficientC(f, n) decreases as the cumulative number of times of discardingoccurrences d increases.

Third Embodiment

FIG. 4 illustrates an outline of updating the correction coefficientC(f, n) in a third embodiment.

In FIG. 4 , the horizontal axis represents the cumulative number oftimes of discarding occurrences d. The vertical axis is the correctioncoefficient C(f, n) collected for the flow ID: f from SW #n, where thecorrection coefficient is α for a cumulative number of times ofdiscarding occurrences d of 1 and increases by β each time thecumulative number of times of discarding occurrences d increases by 1.Accordingly, the correction coefficient C(f, n) is given by thefollowing equation.d=1:C(f,n)=αd≥2:C(f,n)=min(1, α+d×β)

Here, α and β are both predetermined values, and for example, arerepresented asα=δ/γβ=(1−α)/(N−1)where γ [s] is a collection time interval of the amount of discardeddata, δ [s] is an average length of microbursts, and N is the cumulativenumber of times of discarding occurrences when the correctioncoefficient C(f, n) reaches the upper limit of 1. In addition, α<β<1may be set.

Further, the value to be added to the correction coefficient C(f, n)each time the cumulative number of times of discarding occurrences dincreases is not limited to the fixed value β, and may be, for example,β2 to βN that gradually increase as in the second embodiment. Further,the correction coefficient C(f, n) may be a for a cumulative number ofdiscarding occurrences d of 1, and may be d×β for a cumulative number ofdiscarding occurrences d of 2 or more.

Fourth Embodiment

In the first to third embodiments, when the amount of discarded datacollected for each flow ID from each SW reaches 0, incrementing thecumulative number of times of discarding occurrences d is stopped, andthe cumulative number of times of discarding occurrences d is reset to 0when the correction coefficient C(f, n) exceeds 1.

In a fourth embodiment, the number of times the amount of collecteddiscarded data becomes 0 continuously is incremented, and when thecumulative number of that times (the cumulative number of not-discardingoccurrences) exceeds M, the cumulative number of times of discardingoccurrences d is decremented, and then the correction coefficient C(f,n) corresponding to the cumulative number of times of discardingoccurrences d is updated. This makes it possible to prevent a situationin which a traffic condition in which discarded data no longer occurswith time is continuously taken into consideration.

Fifth Embodiment

FIG. 5 illustrates an outline of updating the correction coefficientC(f, n) in a fifth embodiment.

In FIG. 5 , in the fifth embodiment, basically as in the firstembodiment, the correction coefficient C(f, n) increases by 3 accordingto the cumulative number of times of discarding occurrences d, but thecumulative number of times of discarding occurrences d is reset to 0when the amount of collected discarded data reaches 0. In addition, avalue obtained by subtracting a predetermined value ε from thecorrection coefficient C(f, n) at that time is set as an initial value,and a step width for the correction coefficient C(f, n) that increasesaccording to the cumulative number of times of discarding occurrences dis set to β′ which is smaller than β. Hereinafter, the above processingis repeated each time the amount of collected discarded data reaches 0.

Here, the determination as to whether or not the amount of discardeddata reaches 0 is when the amount of discarded data indicates 0continuously for a predetermined period. The predetermined period is,for example, a value obtained by adding a predetermined value V to anaverage of periods for which no data discarding occurs.

OTHER EMBODIMENTS

Although the embodiments of the present invention have been describedabove, the present invention is not limited to the above-describedembodiments, and can be implemented by any combination of theembodiments without being inconsistent.

Further, the SWs and L2NWC making up the L2NW in each embodiment mayeach be provided as a general-purpose computer. In that case, a programfor implementing their functions may be recorded on a computer-readablerecording medium, and the program recorded on the recording medium maybe read and executed by a computer system. Note that the term “computersystem” as used herein includes an OS and hardware such as a peripheraldevices. Further, the “computer-readable recording medium” refers to aportable medium such as a flexible disk, a magneto-optical disk, a ROM,or a CD-ROM, or a storage device such as a hard disk built in thecomputer system. Further, a “computer-readable recording medium” mayinclude anything that dynamically holds the program for a short periodof time, for example, a communication line for transmitting a programvia a network such as the Internet or a telecommunication line such as atelephone line, and anything that holds the program for a certain periodof time, such as a volatile memory included in the computer system thatserves as a server or a client in that case. Further, the above programmay be for implementing a part of the above-mentioned functions, may befurther provided as any combination of a program already recorded in thecomputer system for implementing the above-mentioned functions, or maybe implemented by using hardware such as PLD (Programmable Logic Device)or FPGA (Field Programmable Gate Array).

REFERENCE SIGNS LIST

-   11 Correction processing unit-   12 Adjustment processing unit

The invention claimed is:
 1. A communication control system comprising:a plurality of layer 2 switches (hereinafter, referred to as SWs); and acommunication control device that controls communication of the SWs,wherein each SW includes: one or more queues that each have a variablequeue length for accumulating input frames; and a transmission unit thathas a shaping function of transmitting the frames accumulated in thequeues to a desired destination at a desired rate, and the communicationcontrol device includes: a correction processing unit that acquires anamount of discarded data generated in each queue of the SW, andmultiplies the acquired amount of discarded data by a correctioncoefficient weighted by the cumulative number of times of discardingoccurrences for which the amount of discarded data is not 0 to obtain acorrected amount of discarded data; and an adjustment processing unitthat determines adjustment values for the queue length of each queue andshaping rate of the SW based on the corrected amount of discarded data,and notifies each SW of the adjustment values.
 2. The communicationcontrol system according to claim 1, wherein the correction coefficientis managed for each SW and for each queue, and is a value with an upperlimit of 1 that increases by β (β<1) each time the cumulative number oftimes of discarding occurrences increases.
 3. The communication controlsystem according to claim 2, wherein the correction coefficient is αsmaller than the β when the cumulative number of times of discardingoccurrences is
 1. 4. The communication control system according to claim1, wherein the correction coefficient is managed for each SW and foreach queue, and is a value with an upper limit of 1 that increases by βdaccording to the cumulative number of times of discarding occurrences d,andβ1<β2<. . . <β(N−1)<βN or β1>β2>. . . >β(N−1)>βN is set, where N is thecumulative number of times of discarding occurrences when the correctioncoefficient reaches
 1. 5. The communication control system according toclaim 1, wherein the correction processing unit performs processing ofstopping incrementing the cumulative number of times of discardingoccurrences when the amount of discarded data becomes 0, and ofdecrementing the cumulative number of times of discarding occurrenceswhen the cumulative number of times of not-discarding occurrences inwhich the amount of discarded data is 0 exceeds a specified value, afterthe cumulative number of times of discarding occurrences reaches 1 ormore.
 6. The communication control system according to claim 1, whereinthe correction processing unit sets as an initial value a correctioncoefficient based on an immediately preceding correction coefficientwhen the amount of discarded data becomes 0, and obtains a correctioncoefficient weighted by the cumulative number of times of discardingoccurrences reset, after the cumulative number of times of discardingoccurrences reaches 1 or more.
 7. A communication control methodperformed by a communication control system including a plurality oflayer 2 switches (hereinafter, referred to as SWs) and a communicationcontrol device that controls communication of the SWs, each SW includingone or more queues that each have a variable queue length foraccumulating input frames, and a transmission unit that has a shapingfunction of transmitting the frames accumulated in the queues to adesired destination at a desired rate, the communication control methodcomprising: by the communication control device, acquiring an amount ofdiscarded data generated in each queue of the SW; multiplying theacquired amount of discarded data by a correction coefficient weightedby the cumulative number of times of discarding occurrences for whichthe amount of discarded data is not 0 to obtain a corrected amount ofdiscarded data; determining adjustment values for the queue length ofeach queue and shaping rate of the SW based on the corrected amount ofdiscarded data; and notifying each SW of the adjustment values.
 8. Acommunication control device for a communication control system thatincludes a plurality of layer 2 switches (hereinafter, referred to asSWs), and the communication control device that controls communicationof the SWs, each SW including one or more queues that each have avariable queue length for accumulating input frames, and a transmissionunit that has a shaping function of transmitting the frames accumulatedin the queues to a desired destination at a desired rate, thecommunication control device being configured to acquire an amount ofdiscarded data generated in each queue of the SW; multiply the acquiredamount of discarded data by a correction coefficient weighted by thecumulative number of times of discarding occurrences for which theamount of discarded data is not 0 to obtain a corrected amount ofdiscarded data; determine adjustment values for the queue length of eachqueue and shaping rate of the SW based on the corrected amount ofdiscarded data; and notify each SW of the adjustment values.